Ion-exchange resins are organic compounds, compounds synthetically polymerized, which contain positively and negatively charged units (ions)--one of the types of ions is readily replaceable by another ionic unit of similar charge from a surrounding solution. The ion-exchange resins are cationic or anionic.
Two separate types of resins, that is, the chelating resins and the electron-exchange resins, are commonly classed as ion-exchange resins. Chelating resins are, for example, styrene-divinylbenzene polymers to which functional iminodiacetate groups are introduced. Such functional group forms complexes with all of the metallic elements except the alkali metals, with stabilities that vary with the different metals.
It is particularly important to remove the long-lived fission product cesium-137 from radioactive wastes. Cesium-137 and strontium-90 are the major radioactive components in the soluble fraction of alkaline defense waste from the Department of Energy's Savannah River Plant. Phenolic ion exchange resins have a high selectivity for cesium even in the presence of large excesses of sodium. See: Baumgarten, P. K., M. A. Ebra, L. L. Kilpatrick, and L. M. Lee, "Ion Exchange Processes for Decontaminating Alkaline Radioactive Waste", presented at Waste Management, '81, Tucson, Arizona (Feb. 23-26, 1981); Wallace, R. M., and R. B. Ferguson, "Development of an Improved Ion-Exchange Process for Removing Cesium and Strontium from High-Level Radioactive Waste", presented at the International Symposium on the Scientific Basis of Nuclear Waste Management, Boston, Mass. (Nov. 16-20, 1980); and Baumgarten, P. K., R. M. Wallace, D. A. Whitehurst, and J. M. Steed, Scientific Basis for Nuclear Waste Management 2, Clyde J. M. Northup, Jr., et al., eds., Plenum Press, Boston, Mass. (1980), pp. 875-884. Currently the Savannah River Plant uses Amberlite.RTM. IRC- 718 (Rohm and Haas Co.), a chelating ion exchange resin, for strontium-90 removal. The chelating group present in the IRC-718 resins is iminodiacetic acid.